Protection of electric systems



J. BIERMANNS PROTECTION OF ELECTRIC SYSTEMS Filed Qan. 8, 1926 Nov. 29, 1927. 1,650,593

Inventor:

Josef B'LePmanns,

HvsAttorneg.

Patented Nov. 29, 1927.

urirr.

1 TBS JOSEF BIEBMIANNS, OF KARLSl-IORST, GER'MANY, ASSIGNOB T GENERAL ELECTRIC COINIPANY, A CORPORATION OF NEW YORK.

EROTEGTION OF ELECTRIC SYSTEIES.

Application filed January 8, 1926, Serial "No. 80,093, and in Germany January 29, 19535.

My invention relates to improvements in the protection of electric systems and more particularly to improvements in protective arrangeu'ients for an electric system having one or more line sections of conductor groups which are connected in parallel and each of which comprises two parallel conductors and a single conductor at each end thereof with suitable circuit interrupters in the single conductors. An object of my invention is to provide an improved protective arrangement whereby the number of circuit interrupters is minimized and special circuit interrupter structures are not required. A further object of my invention is to provide for a system comprising a. plurality of sections, an. improved balanced protective arrangement such that on the occurrence of a fault continuity of service is maintained on the sound sections without dependence on the graded time action of protective relays.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

The single figure of the accompanying drawing illustrates diagrammatically an embodiment of my invention shown in single phase diagram for clearness and as applied to a section of an electric system between two points thereof such as station busses 3 and t which are connected by a. plurality of conductor groups 5 and 6 in parallel. The group 5 comprises two parallel conductors 7 and 8 connected at their ends by single conductors 9 and 10 through circuit interrupters 11 and 12 to the busses 3 and 1 respectively. The group 6 also comprises two parallel conductors 13 and 1 1 connected at their ends by single conductors 15 and 16 through circuit interrupters 17 and 18 to the busscs 3 and 4 respectively. To convey a concept of dis tance between the busses 3 and 4, the intermediate portion of each of the conductors 7, 8,13 and 1 1 is shown in broken line. Trip coils 19 are provided for controlling the opening of the circuit interrupters 11, 12, .17 and 18. The single conductors 9, 10, 15 and 16 may be relatively short in comparison with the lengths of the parallel conductors 7, 8, 13 and 1 1. The parallel conductors 7 and 8, likewise 13 and 14, may be separately strung as overhead parallel lines or mounted in suitable cable forms for either overhead or underground construction, as is well known to the art.

For controlling the circuit interrupters through their trip coils 19 upon the occurrence of faults on the conductors 7, 8, 13 and 1 1-, relays 20, 21, 22 and 23, which are arranged. to control relatively movable con tacts in the circuits of the trip coils, are provided. The relays 20 and 21 are arranged to be energized upon the occurrence of a disturbance in the balance of the cur rents normally carried by the conductors 7 and 8. For this purpose, the relay 20 is connected across equip'otential points of a circuit comprising the secondaries of current transformers 24; and 25 at one end of the conductors 7 and 8, the secondaries being connected in; series normally for circulating current. The relay 21 is likewise connected across equipotential points of a circuit comprising the secondaries of current transformers 26 and 27 at the other end of the conductors 7 and 8, the secondaries being connected in series normally for circulating current. The relays 22 and 23 are similarly connected in circuits comprising the secondaries of current transformers 28, 29, 30 and 31 in the conductors 13 and 1 1. It is assumed that the conductors '7 and 8 no mally carry equal currents and that the ratios of each of the current transformers are the same and similarly for the conductors 13 and 1 1'. If theconductors of a pair normally do not carry equal currents, the ratios of the current transformers may be so proportioned as to provide equal secondary currents in normal operation.

If new a fault occurs in the conductor group 5 at a point such as 32, the current in the secondary of the current transformer 2'? becomes greater than the current in the secondaries of the current transformers 26 and 24. Under the effect of the difference currents in the respective pairs of current transformers the relays 20 and 21' operate to control the circuit interrupters 11 and 12 and thus to open the circuit of the conductor group at fault. If, however, the fault occurs near one end of a conductor group at a point such as '33, there will be a difference between the currents in the secondaries of the current transformers 2 1 and 25 and the relay 20 will operate to effect the opening of the circuit interrupter 11, but the currents in the secondaries of the current transformers 26 and 27 will not materially differ and therefore the relay 21 will not operate. Consequently the fault will continue to he fedthrough the circuitinterrupter 12.

In order to avoid this difficulty, I provide in accordance with my invention means for selective controlling the circuit interrupt ers 11, 12. 17, and 18 in the single conductors 9, 10, 1o, and 1-6 respectively so as to maintain continuity oi? service on sound sections on the occurrence of faults and particularly through faults independently of graded. llllTlO relay settings. This means, shown, comprises relays 12 and l3-wluchare arranged to he energized in accorc ance with the dil'l'erences between the currents in the single conductors 11 and 15, and and 16, respectively.

The relays 42 and l3 may he of any suit able selective type, examples of which are well known to the art. is illustrated, they comprise cooperating current and potential windings l. and respectively, arranged to control suitable circuit controlling members 16 which are movable in one direction or the oypositethereto according to the direction oi? the current in the winding 14. The current winding 1-5: of relay 1-2 is arianged to he energized in accordance with the difference hetween the currents in the single conductors 9 and 15, that is, the difference between the sum of the currents in the conductors 7 and 8 and the sum of the en :rents in the conductors 13 and 1 1. For this purpose the winding 1 1 is connected across equipotential points oi a circuit in which the secondaries of current transformers l7 and 18, arranger. in the single conductors 9 and 15, are con nected in series normally for circulating cur- The current winding 44s of relay 13 is, for a like purpose, similarly connected in a circuit comprising the secondaries ()Tll current transformers 19 and arranged in the single conductors 10 and 16. The potential windings o1? relays 12 and 4L3 arranged to he energized from the husses 3 and through potential transformers 51, 52 rec 'vely.

.lhe relay 4-2 is so arranged that, when the current in the single conductor 9 exceeds the current in the single conductor 15 by a predetermined valuc, the contact controlling ,met'uher 4L6 will he moved to the left to C0111- the circuit of the trip coil 19 of the circuit interrupter ll-and when the current in the conductor 15 exceeds the current in the conductor 9, the contact controlling n'iemher 4-6 will. he moved to the right to complete the circuit of the trip coil 19 of the circuit interrupter 15. Similarly, if the current in the single conductor 10 or 16 exceeds the current in. the single conductor 16 or 10, respectively, by a predetermined value, the relay 13 will ellectthe opening oi" the circuit interrupter 12 or 18 respective it, new, a fault should occur on one of the twin or parallel conductors 7 and 8 at a point such as 33, the relay 20 will elicct the opening of circuit interrupter 11 as heretofore described. tllhe current in the single conductor 10 will now exceed the current in the single conductor 16 and t e dilicrcnce hetwe n these currents will through the windingi l of the relay "51-33 in such a direction as to more the conta ,t controlling memher all) to the lct't and thereby to compl 'te the ciri 't of the trip coil 1a the circuit interrupter he relays ll-E2 and LI-l may he arranged to hayv a time delay action longer than that oi the l 2h, 21, 2 22 and 2 so that the latter we: -c care oil? i'aulls at points such as 23; while in case of faults at points such as 32-3 the relays is or 412;- would operate to trip the desired circuit interrupter only after the relays 20, E21, or had ope ited. 'ihereiorc, with an electric system which comprises a phirality of interconnected sections sin'iilarly relayed, through faults irrespective of their intensity can not impair continuity oi service on sound sections of the system since the operation of the relays 4:2 and 43 is dependent on the balance it the currents in the single conductors, that is, the difference between the currents and is independent of graded time actions.

What I claim as new and desire to secure by Letters Patent oi? the United States, is,

1. In a protectivearrangement:lFor an electric system wherein a plurality of con due-tors are connected in pairs and wherein circuit interrupterc are arranged for connecting said pairs in parallel, relay means for controlling the circuit interrupter-s of one pair of: conductors connected and arranged to he energized in accordance with the difference between the currents in the conductors of said pair, and. relay means for selectively cmitrolliug the circuit interrupter-s of two pairs of conductors connected and an ranged to he energized in accordance with the dilierence between the sum oi the cur-- rents in the conductors of one olf said two pairs and, the sum cit the currents in the condirirtors of the other of said two iairs.

2.111 a protective arrangement for an electric system wherein a plurality of conductors are connected in pairs and wherein circuit interrupters are arranged for connecting said pairs in parallel, relay means associated with each pair for controlling the circuit interrupter hereof connected and arranged to he energized in accordance with the difference between the currents in the conductors of the associated pair, and relay means I iOi' selectively controlling the circuit interrupters of two pairs of conductors connected and arranged to he energized in accordance with the difference between the currents traversing said circuit interrupters.

3. In a protective arrangement for a section of an electric system wherein conductor groups comprising .two parallel conductors and a single conductor at each end thereof are connected in parallel and wherein circuit interrupters are arranged in the single conductors, means associated with two par allel conductors at one end thereof for controlling the circuit interrupters in the single conductor at that end in accordance with the di'li'erence between the currents in the two parallel conductors, and means for :wlectively controlling the circuit interrupters in two single conductors at one end of the section connected and arranged to be energized in accordance with the difference between the currents in the two single conductors.

4%. In a protective arrangement for a section of an electric system wherein two c 0nductor groups, each comprising two parallel conductors and a single conductor at each end thereof, are connected in parallel and wherein circuit interrupters are arranged in the single conductors, means associated with the two parallel conductors of each group at the ends thereof for controlling the circuit interrupter in the single conductor of the group comprising a relay arranged to be energized in accordance with the difference between the currents in the two parallel conductors, and means at the ends of the section for selectively controlling the circuit interrupters in two single conductors comprising); a relay arranged to be energized in accord.- ance with the difference between the currents in the two single conductors.

In witness whereof, I have hereunto set my hand this 18th day of December, 1925.

J OSEF BIERMANNS. 

